Wireless networks aim to increase rates and amounts of data through the networks to allow for more users, more or enhanced services and/or faster transmission times.
Already during their deployment, current 4G mobile communications systems (like LTE-Advanced) appear to suffer from a shortage of data rate that can be provided to the users. It is expected that in the future, the data rate requested by the users grows considerably, which is mainly due to reception of video contents. There is a trend to an increased consumption of non-linear TV/video, i.e., video contents that is not being broadcast at the very moment of its consumption. Besides broadcast contents that is consumed at some later point after its transmission (like the offering of the TV channels' media centers) and that could be stored inside a cache in the user equipment (UE) until its consumption, there is a vast realm of content that cannot simply be distributed by conventional broadcast systems (satellite, terrestrial, cable TV) like YouTube videos. At the same time the contents consumed in the homes necessitates increasingly high data rate, for instance for Ultra High Definition TV (UHDTV) or 3D contents (with or without dedicated 3D-glasses).
Moreover, people exchange, i.e., down and upload increasingly large files. While this is currently photos of a couple of megabytes, people are going to download complete movies of many gigabytes from their mobile devices in the future. For such actions people are keen to keep the download times as short as possible, such that very high data rates in the order of ten gigabit/s are a realistic requirement for the future. As people are going to use cloud services to a greater extent in the future, there will be a need for fast synchronization of the contents on a mobile device with the cloud when people leave or enter the coverage of a mobile network, i.e. before they go off-line and after they return from on off-line state. The amount of data to synchronize could be quite large. All of this shows that transmission at very high data rates may be regarded as a requirement in the future for many (mobile and stationary) devices.
An alternative to using mobile communications like LTE for downloading such large files is the employment of a local area network (LAN), be it wireless (WLAN, W-Fi) or wired (Ethernet). However, the last mile from the backbone network to the homes cannot support the necessitated high data rates in the range of Gbit/s, except if optical fibers are used (fiber-to-the-home FTTH). However, the cost to equip the homes with FTTH is very high; for instance for Germany alone, the cost to equip every building with FTTH is estimated around 93 billion/milliard Euros. Therefore, we reckon that the last mile will eventually become a mainly wireless connection. This reduces the cost for bringing broadband to every building and its rooms significantly.
Moreover, most homes do not possess a dedicated wired LAN infrastructure (Ethernet) to distribute the data received over the last mile further, i.e., most homes employ Wi-Fi to connect their devices to the Internet by their access point (AP), where the AP represents the terminal point of the last mile. It should be observed that for reaching data rates of Gbit/s, either an Ethernet socket or an AP is present in one more or each room of every home or office building. Hence the cost of connecting each room of each building have to be added to the figure mentioned above for connecting the buildings.
Further the main structures of a network topology are centralized (e.g., IEEE802.11) or distributed (e.g., mobile ad hoc networks such as defined in IEEE802.15, which are also called piconets).
In a centralized architecture only the coordinating device is responsible for discovery and all the data traffic is routed through this device. In a distributed system there also exists peer to peer communication and discovery is supported, which may but not need to be independent of a coordinating device.
The upcoming standard IEEE802.11ad supports, as far as published yet, centralized and distributed structures. The distributed structures are also referred to as adhoc-peer to peer, independent basic service set (IBSS) and/or personal basic service set (PBSS). For discovery 3 low rate physical layer (LRP) channels per 2.16 GHz band are used for beacon transmission. FIG. 25 shows a frequency allocation by channel type as it is proposed in the IEEE802.11ad standard. The LRP frequencies are fixed. The discovery is based on beacon data transmissions by the device that wants to be discovered. In [1] it is proposed that IEEE802.11b,g,n or IEEE802.11a transmissions may be used to help in scheduling and managing the IEEE802.11ad devices. Directional relaying services are also planned for IEEE802.11ad. These will incorporate decode and forward methods. IEEE802.11 networks are using Time Division Duplex (TDD) for transmissions with or without acknowledgement. The initial synchronization on the time structure is done via carrier sense multiple access with collision avoidance (CSMA-CA).
In [2] it is described, how piconets as defined in IEEE802.15 are created and managed. A beacon is presented by the piconet coordinator (PNC) to which further devices in the network synchronize in time and frequency. As asynchronous discovery and communication, typically some implementation of the ALOHA protocol, as it is described in [3] is used. Provided by the PNC is a single framing structure (superframe) that is shared by the whole piconet. Within that a certain period of time is reserved for asynchronous transmissions, all other transmissions are scheduled by the PNC. Methods for dynamically changing the network layout or switching the PNC are defined. Also the scanning of frequency ranges for interference, beacons and channel quality is supported. The PNC decides on the single used frequency in the network (which may change over time to adjust to the interference conditions). Adhoc networks typically do not use the extremely-high frequency (EHF) band as the attenuation of the signals is very high in this frequency range and only line of sight (LOS)-transmissions are possible, wherein [4] provides an extension for mm-waves.
The main challenge for distributed mobile adhoc networks (MANETs) is the solving of the routing problem. For this the received data has to be analyzed and at least the routing relevant information has to be extracted. Adhoc networks are usually very sensitive in the scope of power consumption and they provide sophisticated mechanisms for sleep mode and for how to recover from that while still keeping the network information. There are implementations on localizing the partners in the network to allow the use of beamforming.
For all the realizations discussed above it is common that they are designed to provide a point to point reliability of data transmission. This is ensured by different scheduling and data-acquisition schemes. For example, this may be a common control channel for all devices.
In the state of the art systems frequency, time, code and space are seen as the limited resources that are to be shared and allocated in the best possible way. This is done for one device, be it a real central management unit or a local PNC.